It is often necesssary to join fine wires of refractory metals in electron tube structures. Methods using a second metal or material are undesirable for the properties of the alloyed joints they produce. Similarly, it is often desired to join ceramics without the use of cements or solders to avoid the contamination that the intervening material introduces.
In one prior art method, nickel plated thoriated tungsten wires are wrapped tightly onto an alumina mandrel to form a mesh. The ends of the mesh are held onto the mandrel with nickel plated tungsten and molybdenum tie wires while the mesh is diffused in a hydrogen furnace at 1350.degree. C. In the furnace the nickel plating diffuses into the tungsten, forming bonds between the crossing wires. This procedure has the disadvantage that the nickel must be evaporated from the wire before carburizing, and while doing so, some Ni atoms diffuse into the tungsten. These foreign atoms lower the recrystallization temperature of the tungsten, embrittle the wire, and lowers the strength of the wire.
Another prior art method uses spot welding of wires at their intersections. This method, as shown in U.S. Pat. Nos. 3,737,711 and 3,724,424 introduces considerable strain because of the deformation from welding distorts the mesh.